1. Field of the Invention
The present invention relates to a memory device for storing information by accumulating electrical charges moved from a conduction region for memory in a storage region and a manufacturing method thereof, and an integrated circuit thereof for integrating such memory devices. More specifically, the present invention relates to a memory device having the conduction region for memory formed on an insulator and a manufacturing method thereof, and an integrated circuit thereof for integrating such memory devices.
2. Description of the Related Art
A typical memory device according to the related art, EEPROM (Electrically Erasable Programmable Read-Only Memory) or flash memory, for instance, is provided with a layer of storage region between a memory gate electrode and a conduction region. The storage region stores information by accumulating electrical charges (that is, electrons or holes) moved from the conduction region to this storage region by tunnel effects. The insulating film between the conduction region and the storage region has been formed hitherto by thermal-oxidation of the surface of the conduction region made of silicon (Si) at a high temperature in the range of 800-1000.degree. C.
As described above, in the memory device according to the related art, the insulating film has been formed by heat treatment at a high temperature. As a result, the memory device is unable to be formed on a substrate made of insulator such as silicate glass, quartz glass or plastics, which have a low melting point.
On the other hand, if we try to form the insulating film by thermal oxidation at a low temperature of 500.degree. C. or lower, high insulation performance cannot be achieved. In addition, electrical charges accumulated in the storage region leak to the conduction region in a short time through a large amount of defects in the insulating film, and thus the information is unable to be stored over a long period of time.
It is therefore an object of the present invention to provide a memory device which can store information over a long period of time even when it is manufactured at low temperatures and a manufacturing method thereof, and an integrated circuit for integrating such memory devices.